1. Field of the Invention
The present invention relates generally to a heat dissipation structure and a handheld electronic device with the heat dissipation structure, and more particularly to a heat dissipation structure applicable to a handheld electronic device for enhancing the heat dissipation performance thereof.
2. Description of the Related Art
In recent years, along with the rapid development of electronic industries, the operation speed of the electronic components in a handheld mobile device has been continuously enhanced. In operation, the electronic components will generate a great amount of heat to lead to rise of temperature of the electronic components themselves and the entire system. This will affect the stability of the system. In order to ensure normal operation of the electronic components, generally a heat dissipation device is mounted on the electronic components to dissipate the heat generated by the electronic components.
Vapor chamber and heat spreader are the currently hottest materials that are applied to the electronic products for dissipating heat. For example, intelligent mobile phones, tablets, LED lights and car-used LED lights have employed these passive heat dissipation measures. The vapor chamber and heat spreader are chosen for the mobile phones, tablets and LED lights mainly for reasons that the vapor chamber and heat spreader are both passive heat dissipation measures, which will not consume energy. Also, the vapor chamber and heat spreader two-dimensionally conduct heat, that is, they conduct heat on a face without being affected by gravity. Moreover, the vapor chamber and heat spreader are suitable for the lightweight, thin and closed design of the electronic products to achieve very good heat dissipation effect.
The vapor chamber works by principle that is substantially identical to the working principle of the heat pipe, including four main steps of conduction, evaporation, convection and condensation. The vapor chamber is a two-phase fluid device formed of a container over which microstructures are distributed. Pure water is filled in the container. The heat is conducted from an external high-temperature section into the vapor chamber. The water around the point heat source will quickly absorb the heat to evaporate into vapor and carry away a great amount of heat. Due to the latent heat of the vapor, when the vapor in the vapor chamber spreads from the high-pressure section to the low-pressure section, (that is, the low-temperature section), to touch the inner wall of lower temperature, the vapor will quickly condense into liquid to release the heat. The condensed water flows back to the heat source under capillary attraction of the microstructures to complete a heat transfer cycle. Accordingly, a two-phase circulation system of water and vapor exists in the vapor chamber. The water in the vapor chamber continuously evaporates. The pressure in the chamber will keep balanced along with the change of the temperature. In a low-temperature state, the heat conductivity of the water is lower. However, the viscosity of the water will change along with the change of the temperature. Therefore, the vapor chamber is able to operate at 5° C. or 10° C. The liquid flows back by means of capillary attraction so that the affection of gravity to the vapor chamber is relatively small. Accordingly, the system can be designed to be arranged in any angular position. The vapor chamber is a totally passive and closed device free from any power supply or any movable element.
The housing of the vapor chamber needs anodization to avoid oxidization due to contact with air. The anodization will lead to an additional thermal resistant layer, which will deteriorate heat dissipation efficiency. To overcome this problem, the vapor chamber can be coated with soft ceramic heat dissipation paint instead of the anodization. Especially, in the case that the vapor chamber is coated with white soft ceramic heat dissipation paint, the thermal resistance of such heat dissipation paint is nearly down to zero and such heat dissipation paint is able to protect the housing of the vapor chamber from oxidization. Under such circumstance, the vapor chamber can achieve an excellent cooling effect.
In addition, currently, graphite heat spreader is employed as a heat dissipation component. The graphite heat spreader is a nano-complex material for uniformly conducting heat on a surface. The graphite heat spreader has EMI shielding effect and unique grain orientation for bidirectionally uniformly conducting heat. The graphite heat spreader has laminated structure, which is well applicable to any surface.
The chemical composition of the graphite heat spreader is mainly pure carbon element C, which is a natural mineral element. The graphitized film is achievable at high temperature and high pressure by means of chemical method. Carbon element is a nonmetal element. However, it has electro-conductivity and heat conductivity as a metal material. Moreover, carbon element has plasticity similar to organic plastic. In addition, it has many excellent working performances including special thermal performance, chemical stability and lubrication and is applied to the surface of a solid body. The graphite heat spreader has a super-high heat conduction performance within 150-1500 W/mK on a plane (horizontal heat conduction). Furthermore, the vertical thermal conductivity of graphite is only 5-20 W/mK. That is, graphite is nearly thermally isolative in vertical direction. Accordingly, the graphite heat spreader is characterized in that it has a horizontal thermal conductivity much higher than that of other metals and a quite low vertical thermal conductivity.
Also, the graphite heat spreader is mainly characterized by super-high thermal conductivity, easy operation, low thermal resistance and lightweight. Thanks to the plasticity of graphite, the graphite material can be formed into a film like an attachment sheet. The film can be attached onto the circuit board inside a mobile phone to isolate the components from contacting each other and provide a shock absorption effect. The graphite heat spreader has higher horizontal thermal conductivity so that it can quickly conduct heat in horizontal direction to uniformly distribute the heat over the entire surface and eliminate a local hot point. To speak more precisely, the graphite heat spreader is able to conduct heat and uniformly distribute the heat, that is, the graphite heat spreader is able to indirectly dissipate the heat.
However, no matter how light the graphite heat spreader is and no matter how thin the graphite heat spreader is, when the graphite heat spreader is installed in the mobile device, it still inevitably occupies a certain space. Therefore, in order to truly achieve the object of lightweight and thin internal space of the mobile device, it is tried by the applicant to provide a modified heat dissipation structure applicable to the existent mobile phone so as to effectively solve heat dissipation problem thereof.